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Mold under wallpaper

My contractor removed wallpaper from a bedroom in preparation for repairing plaster and painting. The wallpaper has been in place for about 20 years. When he pulled the backing off, all 4 walls were covered in mold very evenly except right where the strips joined. There is no water source nearby and none of the other wallpapered rooms had that problem.

We are speculating that the paper hanger may have used some paste that had been opened and not resealed well allowing mold spores to develop. Has anyone come across this before? Any other ideas as to the cause?

Re: Mold under wallpaper

Mold loves cool, dark, humid areas. You don't neccessarily need wetting of the surface, but merely subjecting it to relatively high humidity.
One source of humidity could be two breathing adults sleeping in a cool bedroom with the door closed. An adult gives off close to a gallon of water a day while breathing.

Over the years, I noticed that wooden windows in bedrooms would often be the ones in the worst shape in the house. In cold climates, the windows would sweat because of the relatively high humidity there, as opposed to the rest of the house.

Most wallpaper pastes do contain mildecides, although given the proper conditions, it will still support mildew.

It is somewhat curious that the mold was everywhere and not just on the cooler exterior walls.I often found mildew behind bathroom wallpaper, especially on the cold outside walls. Ironically, the plastic coatings on modern washable wallcoverings seems to actually make the problem worse. One would expect that it would keep moisture from reaching the wall surface, but it seems to trap it there.

How old is your house? How much insulation is in the walls and what type of vapor barriers?

Re: Mold under wallpaper

I might add that wallcoverings that are absolute moister barriers, such as foils and mylars, are not a good idea. They constitute an absolute vapor barrier on the inside wall with the possibility of trapping moisture in the wall cavity.

I have personally witnessed such walls where the drywall and insulation were totally bad due to the moisture trapped in the wall. The entire drywall and insulation had to be replaced. In this case, porous brick on the exterior had been passing moisture into the wall cavity where it was trapped by the wallpaper inside.

Re: Mold under wallpaper

BINZ will take care of it!

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